1. Field Of The Invention
This invention relates to inflation and grouting systems for offshore drilling platforms and the like, and more particularly, to such a system having grout and inflation control valves which use pressure balancing to prevent inadvertent opening by hydrostatic pressure in the grout or inflation lines.
2. Description Of The Prior Art
On offshore drilling platforms, it is necessary to secure the legs of the platform to the ocean floor, and a number of methods have been developed to do this. In the typical procedure, a plurality of jacket legs are set on bottom. Each jacket leg is flanked by a plurality of skirt jackets or sleeves which are attached to the jacket leg and set on bottom at substantially the same time as an assembly. The jacket leg is a structural member of the offshore platform or tower that extends from the sea bottom to the working deck above sea level. The skirt jacket or sleeve is a jacket or sleeve which is structurally attached to the jacket leg and extends only partially from the sea bottom toward sea level. After the jacket leg and skirt sleeves are set on bottom, piles are driven through each into the sea bed. The pile is smaller in diameter so that an annulus is defined therearound. A leg pile is any pile placed through the jacket leg, and a skirt or sleeve pile is any pile placed through the skirt jacket or sleeve.
A similar structure is found on the more recently developed tension leg platforms. With these platforms, a template is positioned on the ocean floor with a floating platform located thereabove. Anchoring members extend from the platform to the template to hold the platform in its operating position. The anchor members are always in tension and allow some side-to-side movement of the platform, although the platform is prevented from rising and falling with the swells of the ocean. The tension leg platform template has a plurality of skirt sleeves. There are no jacket legs. As with a conventional offshore platform, piles are driven into the skirt sleeves such that an annulus is defined between each pile and the corresponding skirt sleeve.
Inflation packers are positioned in the annulus at the bottom of each jacket leg and skirt sleeve and are inflated once the piles are in place. The inflated packers bridge the gap between the pile and jacket leg or skirt sleeve, sealing the lower end of the annular space formed therebetween. Grout is then pumped into the annular space between the pile and jacket leg or skirt sleeve to fill the annular space and displace the water therein. The grout enters above the packer.
U.S. Pat. No. 4,140,426 to Knox, assigned to the assignee of the present invention, discloses a system for inflating packers and placing grout through one line in offshore platforms. This prior art apparatus includes a sleeve valve which is the same type of valve identified herein as a sleeve grouting valve. The Knox apparatus includes inflation check and control valves and grout check and control valves. In one prior art embodiment, the inflation check and control valves are contained in one integrated body. However, whether in an integrated body or as separate components, the function is substantially identical.
U.S. Pat. No. 4,275,976 to Knox and Sullaway, also assigned to the assignee of the present invention, shows another inflation and grout system which uses essentially the same components as the Knox patent, but also includes separate inflation and grout lines.
The prior art grout control valves shown in the Knox patent and the Knox and Sullaway patent are pressure actuated valves located near the bottom of the grout lines at the point where the corresponding line enters a jacket leg or skirt sleeve. The valves prevent water from flooding the jacket leg or skirt sleeve should the grout line develop a leak, rupture, or be torn off the platform or jacket during launch or installation thereof. The prior art grout control valves compare a piston held inside a body with a shear pin. The piston closes off the grout line to the jacket leg or skirt sleeve. The piston and shear pin are individually sized for the water depth at which the valve will be used so the pressure will not shift if exposed to hydrostatic pressure. The top of the piston is exposed to the pressure in the grout line, and the bottom of the piston is exposed to the pressure in the leg or skirt sleeve. The grout lines, jacket legs and skirt sleeves are sealed to provide flotation for the platform or template during launch and installation. The pressure inside the grout lines, jacket legs and skirt sleeves is typically atmospheric.
If the grout line develops a leak, ruptures, or is torn off, the top of the piston becomes exposed to hydrostatic pressure and is pushed against the shear pin. The shear pin prevents the piston from shifting and allowing water to prematurely flood the jacket leg or skirt sleeve. Premature flooding of the jacket leg or skirt sleeve can cause the platform or template to sink.
During normal grouting operations, the grout line is filled with water or grout, and pressure is applied to shift the piston. A loss of pressure in the line indicates when the shear pin is sheared and the piston shifted, thereby opening the grout line to the jacket leg or skirt sleeve. Grout can then be pumped into the jacket leg or skirt sleeve.
The prior art inflation check valve and inflation control valve are pressure actuated valves, and as previously indicated, may be in the form of a pressure actuated combination valve. The valves are located on the outside of jacket legs or skirt sleeves adjacent to the packers. The inflation control valves are in communication with the packers and are connected to packer inflation lines. The inflation control valves prevent water from prematurely inflating the packer should the inflation line develop a leak, rupture or be torn off the platform or template during launch or installation thereof. Because initially there is not a pile in place for the packer to inflate against, the packer will burst and the jacket leg or skirt sleeve will be flooded if the packer is prematurely inflated. Inflation control valves also prevent the inflation pressure in the packer from bleeding off if there were to be a leak in the inflation line.
The prior art inflation control valve comprises a piston held inside a body with a shear pin, similar to the grout control valve previously described. The piston in the inflation control valve closes off the inflation line to the packer. The piston and shear pin are individually sized for the water depth at which the valve will be used so the piston will not shift if exposed to hydrostatic pressure. In a manner similar to the grout control valve, the top of the piston in the inflation control valve is exposed to the pressure in the inflation line, and the bottom of the piston is exposed to the pressure between it and the inflation check valve, which is the same as the original pressure in the packer. The initial pressure inside the inflation lines and packers is typically atmospheric.
The prior art inflation check valve is a spring actuated poppet type valve. It opens to allow the inflation fluid to flow into, and inflate, the packer, then closes off to retain the inflation pressure in the packer should the pressure in the inflation line drop.
If the inflation line develops a leak, ruptures or is torn off, the top of the piston in the inflation control valve becomes exposed to hydrostatic pressure and is pushed against the shear pin. The shear pin prevents the piston from shifting and allowing water to prematurely inflate the packer.
Under normal conditions, the inflation line is filled with water or compressed gas, and pressure is applied to shift the piston in the inflation control valve, shearing the shear pin and opening the inflation line to the packer. Water or compressed gas can then be pumped past the inflation check valve into the packer to inflate it against the previously driven pile.
Both the prior art grout control valve and prior art inflation control valve rely completely on the shear pin to keep the piston in the control valve from shifting if the piston is exposed to hydrostatic pressure. If a valve is mishandled during shipment, installation or launch, the shear pin may be damaged enough to allow the piston to shift prematurely if exposed to hydrostatic pressure. Also, materials used to make the shear pin may degrade over time, causing reduction in the shear strength of the shear pin and allowing the piston to shift prematurely if exposed to hydrostatic pressure.
The improved control valve of the present invention is designed so that hydrostatic pressure in the grout line cannot shift the piston because the bottom of the piston is always exposed to hydrostatic pressure. Further, in the present invention, if the piston were shifted before or during launch of the jacket, the hydrostatic pressure will shift the piston back to its closed position. In the inflation control valve, a spring force is also applied to the piston. In the inflation valve of the present invention, the inflation check valve is built into the piston of the inflation control valve, thus greatly simplifying the assembly and eliminating the need for separate valves.